1. Field of the Invention
The present invention relates generally to apparatus and method for selectively providing traction to a wheeled vehicle, and more particularly, to a method and apparatus utilizing a device mounted to or adjacent to the wheel which device may alternatively be engaged to rotate with the wheel and provide traction bars, or lugs, on the periphery of the wheel or, alternatively, be retracted into a stored configuration adjacent the wheel. 2. Description of the Prior Art
Classically, traction enhancing apparatus for wheeled vehicles have involved permanently mounted traction bars, such as lugs on snow tires or tractor tires, or manually mounted removable traction means such as tire chains.
As an improvement to these classical approaches, my U.S. Pat. No. 3,422,870 issued Jan. 21, 1969 disclosed a pantograph linkage rotatably mounted to a backing plate and selectively, extendable to engage and rotate with the tire, or retractable for storage. While this prior concept is basically sound and constitutes a substantial improvement over the classical traction devices, I have now found aspects thereof which are subject to marked improvement. The traction bars of my prior patent device are rigidly attached to the pantogram thus inducing force directly into the rather rigid triangulated pantogram configuration. Further, in the event of a deflated tire or the wheel impacting an obstruction, the pantogram does not readily accommodate localized variation in diameter. By its very nature, the pantogram seeks to maintain all traction bars at the same diameter and thus does not conform to variations in tire diameter. As a result of the use of the pantogram linkage, the prior structure necessarily relied upon the linkage geometry to provide a traction bar diameter corresponding to that of the wheel.